The present invention relates to an integrated metal-and-plastic molded article and a method for manufacturing the integrated metal-and-plastic molded article.
As an integrated metal-and-plastic molded article, stack manifolds attached to ends of fuel cell stacks are known (see Japanese Laid-Open Patent Publication No. 2015-8086). A stack manifold is adapted to selectively supply fluid such as fuel gas, oxidation gas, and coolant to and discharge fluid from the fuel cell stack. The fuel cell stack generates electric power using fuel gas and oxidation gas that are selectively supplied and discharged via the stack manifold and is cooled down by the coolant that is selectively supplied and discharged via the stack manifold.
The stack manifold includes a metal plate (an end plate). The metal plate is attached to an end of the fuel cell stack at a first surface in the thickness direction of the metal plate. Recesses are formed in the first surface when the metal plate is attached to the end of the fuel cell stack, the recesses configure channels adapted to selectively supply fluid such as fuel gas, oxidation gas, and coolant to and discharge fluid from the fuel cell stack. Also, a plastic portion, which insulates the metal plate and the fuel cell stack from each other, is provided on the first surface (including the inner walls of the recesses).
To manufacture the stack manifold, insert molding is performed as will be described. That is, after setting a cast metal plate in a mold, molten plastic is injected into and solidified in the mold, thus forming the plastic portion on the first surface. Since the injection pressure of the plastic acts on the first surface, the metal plate must have a great thickness to tolerate the injection pressure. Specifically, a method for casting a metal plate having a great thickness includes a gravity casting method using gravity to pour molten metal into a casting mold.
As a casting method having higher productivity than the gravity casting method, there is a high-pressure die casting method that applies high pressure to molten metal when the metal is poured into a casting mold. To ensure mass production, there is a demand for manufacturing such metal plates using the high-pressure die casting method. However, to manufacture a metal plate having a great thickness using the high-pressure die casting method, molten metal is poured into a casting mold before the gas in the casting mold is completely discharged. This forms voids (hollow portions) in the obtained metal plate.
To restrain such void formation, the thickness of the metal plate that should be manufactured may be decreased to promote the gas discharge at the time the molten metal is poured into the casting mold. However, this causes a problem. When molten plastic is injected into a mold in which the metal plate is set for insert molding, the injection pressure of the plastic acts on the metal plate in the thickness direction. This may deform the metal plate and thus lower the quality of the product.